1. Technical Field
The present invention relates to a method of determining optimum laser power for recording data on an optical disk, in an optical disk recording apparatus having a plurality of pickups.
2. Background Art
When recording information on a recordable type optical disk such as a DVD, if irradiation energy of a laser beam given to a recording layer is too large or too small, the shape or edge of a formed record mark is subjected to distortion so that a recorded data reproduction characteristic is degraded. Therefore, at the time of data recording, the power of the laser beam needs to be set to a value suitable for writing. However, a laser diode that generates a laser beam has a nature that the wavelength changes depending on a temperature variation, and the output level change due to variation of recording speed is very large. Further, a sensitivity characteristic of a recording layer differs individually per optical disk so that it is not possible to handle all disks with the same writing characteristic. In order to solve this problem, use has conventionally been made of a technique of OPC (recording laser power optimization, Optimum Power Control). In this technique, a test-write area PCA (Power Calibration Area) for performing power calibration is provided on a disk, test writing of test data is once carried out in this test-write area at the time of data recording, a recording power that can achieve a sufficient data reproduction characteristic is derived based on a result of reading the test-written data, and then recording of actual data is performed.
As documents relating to the OPC for the disk, the following are present.
[Patent Document 1]
Unexamined Patent Publication No. Hei 9-212866
[Patent Document 2]
Unexamined Patent Publication No. Hei 8-102069
[Patent Document 3]
Utility Model No. 3059334
Some type of the optical disk recording apparatus is provided with a plurality of optical pickups. When recording or reproducing information on a recordable type optical disk such as a DVD, the plurality of the optical pickups can be operated concurrently or alternately to enhance performance of data recording and data reproducing. However, the conventional OPC of an optical disk recording apparatus having the plurality of pickups may not determine optimal values of laser powers for the respective pickups, because data reading characteristics are different in OPC among the plurality of the pickups. Thus, it is difficult to perform recording of data with the power values optimum for the respective pickups and to equalize β values of the written data over the whole of a disk without receiving an influence caused by a difference in writing characteristic and reading characteristic among the respective pickups.